Process for molding microcellular elastomeric polurethane articles and microcellular elastomeric polyurethanes therefor

ABSTRACT

A novel, particularly flexible, improved process for molding microcellular elastomer polyurethane articles comprises reacting a first type quasi-polyurethane, having a molecular weight of from 600 to 2200 and a free isocyanate group percent content of from 14 to 3.8, with at least one of a second type of quasi-polyurethane, having a molecular weight of from 3000 to 8000 and a free hydroxyl group percent content of from 1.13 to 0.48, and a glycol and optionally in the presence of water. The process according to the invention is particularly well-suited for automation by means of a processor. Also, the preparation of certain microcellular elastomer polyurethanes that are useful in the improved molding process is described.

The instant invention relates to a novel process for molding articles ofmicrocellular elastomeric polyurethane (hereinbelow indicated, for thesake of brevity, simply as M.E.P.). More particularly, the instantinvention relates to a particularly flexible process for molding amicrocellular elastomeric polyurethane.

It is an object of the instant invention to provide a molding processwhich allows one to make a wide range--from the point of view of thephysico-mechanical characteristics--of M.E.P. articles without the needfor changing or substituting the starting materials.

Another object of the instant invention is that of providing a processfor making M.E.P.s particularly suitable for said molding process, inwhich starting materials are employed having a well defined composition.

A further object of the instant invention is that of providing a processfor molding M.E.P. articles wherein the reaction for producing thepolyurethane is driven in a step preceding the molding of the article inorder to form bases with a controlled and stable structure.

A further object yet of the instant invention is that of providing aprocess for molding M.E.P. articles which allows one to make M.E.P.shaving different physico-mechanical characteristics, only by means ofcross-linking agents.

Another important object of the instant invention is to provide aprocess for molding M.E.P. articles which can be automated by means of aprocessor.

These objects and others yet will be more clearly illustrated by thedescription hereinbelow.

As it is known, M.E.P. is generally made by reacting stoichiometricquantities of a polyol and of a prepolymer.

Practically, said reagents are taken from tanks and conveyed to themixing heads by means of dosing pumps. The blending takes place as aresult of the rapid increase of the flow speed of the materialsintroduced into the head, where they flow into one only zone ofrelatively limited dimensions so that there is a very high probabilitythat the molecules of both of the reagents and of the catalyst mayinteract thereby producing a reaction product that is sufficientlyhomogeneous notwithstanding the very high reaction speed. However, foreconomic reasons, very short withdrawal times are demanded in theindustrial process, and, hence, it is necessary to use considerablequantities of catalysts which, by remaining within the finished article,cause the deterioration of the latter's physico-mechanicalcharacteristics.

Furthermore, since the polyols used for making M.E.P. do not consist ofsingle components but instead of mixtures of different components, someof which are hardly or not at all soluble, this gives rise to thedrawback of having to subject the polyol mixtures to homongenizationbefore use. These polyol mixtures must also be constantly stirred duringtheir use.

A further inconvenience of the state of the art processes lies in thefact that the quantity of reagents to be stocked for the molding processmust not only be proportional to the quantity to be worked, but also tothe type of article to be made. This necessitates the interruption ofthe production to allow for changing or modifying one or both reagents(polyol, isocyanate) and/or the catalyst. These changes and/ormodifications, besides lowering productivity, cause the loss of startingmaterials and involve the use of solvents for washing the tanks andequipment. Last but not least, said changes and/or modifications almostalways demand the re-adjustment of the operating conditions of the plantwith the consequent problems of adjusting the production to the marketrequirements.

Evident are the shortcomings of the state of the art processes from whathas briefly been described hereinabove.

Consequently, the object of the instant invention is that of providing aprocess for molding M.E.P. articles, that does not present theshortcomings of the processes known from the state of the art. It hasnow been found that when using strictly defined compounds (hereinaftercalled quasi-polyurethanes or, in short: Q-PUR), as the startingmaterials, instead of prepolymers and polyols, it is possible to makeM.E.P. articles having the specific gravity, surface hardness,elasticity, compressive strength and abrasion resistance of which can bemodified by acting exclusively on the quantity of the startingmaterials.

According to the process of the instant invention, the basic componentsare polymerized to the highest degree compatible with the molding plant.Thus Q-PURs are obtained by means of strictly timed reactions and not byrandom blending in the mixing head.

More precisely, the inventive process provides the use--instead of aprepolymer and of a polyol (which, as is known, is in actual fact amixture of several polyols, sometimes of a not strictly definedcomposition)--of two bases or Q-PURs which not only do not containforeign materials, be they dissolved or not, such as solvents or fillersof various kind, but they have a strictly defined chemical composition.

The first of these bases consists of a quasi-polyurethane (Q-PUR-1) witha molecular weight of between 600 and 2200, preferably between 650 and1500 and even more, preferably between 700 and 1100, and a percentage offree isocyanate (--NCO) groups of between 14 and 3.8, preferably between12.9 and 5.6 and even more preferably between 12 and 7.6. The secondbase consists of a quasi-polyurethane (Q-PUR-2) having a molecularweight of between 3000 and 8000, preferably between 3500 and 5000 andeven more preferably between 3750 and 4500 and with a percentage of freehydroxyl (--OH) groups of between 1.13 and 0.48, preferably of between0.97 and 0.68 and even more preferably between 0.9 and 0.75.

In the blending step, the free --NCO groups of Q-PUR-1 are saturatedwith aqueous glycol solutions and glycol/catalyst solutions so as tomake polyurethane polymers of different specific weight.

The chemical structure of the M.E.P. is modified, according to theprocess of the instant invention, by means of Q-PUR-2. More precisely,said chemical structure varies in proportion to the quantity of Q-PUR-2employed.

According to the instant invention, the isocyanates and the resins arereacted in a vessel according to per se known processes which enablecontrolling the reaction in such a manner as to attain a regulardistribution of the molecular weights.

In the course of the molding step, the glycol develops itschain-lengthening and cross-linking activity. In turn, the Q-PUR-2(which at each extremity of the molecule has a free hydroxyl group)reacts with the Q-PUR-1, via the latter's free isocyanate groups, inorder to form a longer straight chain. In this manner the innerplasticizing of the polymer structure is achieved.

The skilled artisan will immediately appreciate the advantage of usingan inner rather than an external, i.e. an heterogeneous-phaseplasticizing process as that which occurs when conventional (reactive orinert) plasticizers are used. Hence this is a further advantage offeredby the process according to the instant invention.

As already mentioned hereabove, the Q-PUR-1s, suitable for the processaccording to the instant invention, preferably have a molecular weightof between 600 and 2200, preferably between 650 and 1500 and even morepreferably between 700 and 1100 and a percentage of free isocyanategroups ranging between 14 and 3.8, preferably between 12.9 and 5.6 andeven more preferably between 12 and 7.6. This polyurethane resin of theinstant invention is preferably made by reacting a diphenylmethanediisocyanate with a saturated polyester, such as e.g. glycol adipate,having a molecular weight of between 1500 and 2500.

The Q-PUR-1 constitutes the basic component for the M.E.P. formulationand, contrary to what happens with conventional polymers, by saturatingthe isocyanate groups with glycols the whole cross-linking process ofthe system is completed, the final characteristics of which arepredetermined by the type of saturated polyester used, by the molecularweight of Q-PUR-1 as well as by the type of glycol used. The reaction iscatalyzed with triethylene diamine and the specific weight is determinedby the water content.

On the other hand, Q-PUR-2 consists of a polyurethane resin having amolecular weight ranging between 3000 and 8000, preferably between 3500and 5000 and even more preferably between 3750 and 4500, containing apercentage of free hydroxyl groups ranging between 1.13 and 0.48,preferably between 0.97 and 0.68, and even more preferably between 0.9and 0.75. Preferably, this resin is made by reacting, according to perse known methods, diphenylmethane diisocyanate with a saturatedpolyester having a molecular weight of 1500 to 2500, in the molar ratioof 1:2.

The Q-PUR-2 thus obtained constitutes the component capable ofcontrolling the M.E.P. characteristics. As already mentioned one of themain advantages of the inventive process is represented by itsflexibility. In fact, as shown in the Table below herebelow, dependingupon how the various components are combined, it is possible to obtainmolecular structures that differ very much from each other, so much sothat end products can be obtained having completely differentphysico-mechanical characteristics relative to each other. It should notbe overlooked that inside each main group it is possible to arrange forone of the physico-mechanical characteristics to prevail over anotherone.

                                      TABLE 1                                     __________________________________________________________________________     ##STR1##                                                                      ##STR2##                                                                     __________________________________________________________________________

Considering that the reaction partners useful for the instant inventionare all strictly defined materials as far as their chemical compositionsare concerned, the inventive process particularly lends itself toautomation using a processor.

After having generally outlined the process according to the instantinvention, it will now be better illustrated by way of some workingexamples which, for the sake of brevity, do not contemplate all of thestarting materials or the possible reactive combinations thereof. Thisfact, however, shall not constitute a limitation of the scope ofprotection of the instant invention inasmuch--as appears evident to theskilled artisan--the forms of embodiment of the process according to theinstant invention can vary widely, be it with regard to the startingmaterials as to the reaction conditions, so as to adapt them to thespecific circumstances.

Once the skilled artisan has become acquainted with the fundamentalprinciples on which the present process is based, he will have nodifficulty whatsoever in adapting the parameters of the process so as toattain the M.E.P. having the desired characteristics, without therebydeparting from the spirit of the invention.

EXAMPLE 1 Preparation of a quasi-polyurethane using free--NCO groups(Q-PUR-1)

A 10,000 liter steel reaction vessel provided with stirrer,thermoregulator and suitable device for providing an inert environment,is fed with 3751 kg MDI (diphenylmethane diisocyanate) at a temperatureof 38° to 42° C. under stirring and in a dry nitrogen environment, towhich is added 3,748 kg saturated polyester resin (made by reactingadipic acid with monoethylene glycol of m.w.=1500, containing apercentage of water lower than 0.1 and with an acid number lower than 1(AN<1). This resin, at a temperature of 80° C., is fed to the MDI massthrough a line (at the extremity of which is an anti-bubbling continuousflow device) dosed at a flow rate of 70-80 l/min by means of a meteringpump.

Since the reaction is exothermic, the temperature of the reaction masstends to increase, which must therefore be cooled so as not to exceed90° C. After the addition of the resin has been completed, the reactionmass is stirred for 2 hours, between 85° and 90° C., taking care thatthe atmosphere is saturated with nitrogen. The reaction has beencompleted once the following values have been obtained:

free--NCO: 14%

molecular weight: 600

EXAMPLES 2 to 7

By operating in like manner to what is described in Example 1 but usingthe reagents indicated quali/quantitatively in the Table hereinbelow,are prepared the Q-PUR-1s having the characteristics as shown.

                                      TABLE 2                                     __________________________________________________________________________    MDI  RESIN           RESIN   %-NCO                                                                              MOL · WEIGHT                       kg   kg   RESIN (*)  (mol · weight)                                                               (final)                                                                            (final)                                     __________________________________________________________________________    2)                                                                              3280                                                                             4219 monoeth.gly-                                                                             1750    12    700                                                  col/diethyl-                                                                  ene glycol                                                          3)                                                                              2499                                                                             5000 diethylene 2000    8.4  1000                                                  glycol 1/4                                                                    butane diol                                                         4)                                                                              1748                                                                             5751 1/4 butane diol                                                                          2500     5.25                                                                              1600                                        5)                                                                              1532                                                                             5967 1/4 butane diol                                                                          3000     4.66                                                                              1800                                                  moneth.glycol                                                       6)                                                                              1322                                                                             6177 diethylene glycol                                                                        4000    4.2  2000                                                  monoeth.glycol/tri-                                                           methylol propane                                                    7)                                                                              1104                                                                             6395 diethylene glycol                                                                        5000    3.8  2200                                                  trimethylol                                                                   propane                                                             __________________________________________________________________________     (*) Note: "RESIN" stands for a polyester resin made from adipic acid and      the respectively indicated alcohol.                                      

EXAMPLE 8 Preparation of a quasi-polyurethane using free--OH groups(Q-PUR-2)

A 10,000 liter steel reaction vessel provided with stirrer,thermoregulator and suitable device for providing an inert environment,is fed with 8,000 saturated polyester resin (made by reacting, at atemperature of 120° C., adipic acid with monoethylene glycol having am.w.=1500, containing a percentage of water lower than 0.1 and an AN<1).Under stirring and in a dry nitrogen environment is then added, verycautiously, 613 kg MDI, at a temperature of 38° to 42° C., while theflow capacity of the metering pump must not exceed 8 l/min; the bladesof the stirrer must not thrust the MDI against the walls of the reactionvessel.

The environment must be carefully controlled and secured throughout theentire reaction. After the addition has been completed, the reactionmass is left to cool down to 60° C., still under stirring. The reactionhas been completed once the following values are obtained:

free--OH: 1.13%

molecular weight: 3000.

EXAMPLES 9 to 14

By operating in like manner to what is described in Example 8 but usingthe reagents indicated quali/quantitatively in the Table hereinbelow,are prepared the Q-PUR-2s having the characteristics as shown.

                                      TABLE 3                                     __________________________________________________________________________    MDI  RESIN           RESIN   %-OH MOL · WEIGHT                       kg   kg   RESIN (*)  (mol · weight)                                                               (final)                                                                            (final)                                     __________________________________________________________________________     9)                                                                             571                                                                              8000 monoeth.gly-                                                                             1750    0.9  3750                                                  col/diethyl-                                                                  ene glycol                                                          10)                                                                             500                                                                              8000 diethylene 2000    0.8  4250                                                  glycol 1/4                                                                    butane diol                                                         11)                                                                             342                                                                              8000 1/4 butane diol                                                                          2500    0.75 4500                                        12)                                                                             266                                                                              8000 1/4 butane diol                                                                          3000    0.68 5000                                                  monoeth.glycol                                                      13)                                                                             181                                                                              8000 diethylene glycol                                                                        4000    0.56 6000                                                  monoethy.glycol/tri-                                                          methylol propane                                                    14)                                                                              95                                                                              8000 diethylene glycol                                                                        6000    0.48 7000                                                  trimethylol                                                                   propane                                                             __________________________________________________________________________     (*) NOTE: "RESIN" stands for a polyester resin made from adipic acid and      the respectively indicated alcohol.                                      

In Examples 1 thru 14 a polyester has always been employed. However, itis possible to use instead a polyether made--as is known to the skilledartisan--by polymerizing propylene oxide with monoglycols or polyglycolscontaining one or more reactive hydrogen atoms.

Generally, it has been found that the use of polyethers yields Q-PUR-1and Q-PUR-2 having the same molecular weight, yet that are considerablyless viscous than the corresponding quasi-polyurethane originating froma polyester and, hence, having improved workability. At any rate, thechoice depends on the physico-mechanical characteristics of thequasi-polyurethane desired.

EXAMPLES 15 TO 17 Preparation of the "catalyst-foaming agent" solutions

Herebelow is given the composition (the parts are expressed in percent)of three typical solutions having catalytic, chain lengthening anfoaming activity, useful for the process of the instant invention foraffecting the reaction velocity and/or physico-mechanicalcharacteristics of the M.E.P.

    ______________________________________                                                             SOLUTION 2  SOLUTION 3                                   COM-     SOLUTION 1  (chain      (foaming                                     PONENT   (catalyst)  lengthener) agent)                                       ______________________________________                                        Monoethy-                                                                              70          100         70                                           lene glycol                                                                   Dabco    30           0           0                                           Water     0           0          30                                           % Total  100         100         100                                          ______________________________________                                    

The preparation of these solutions does not demand particularprocedures, however the temperature must be kept at about 60° C. andprecaution must be taken to operate in a moisture-free environment.

Dabco, as is known to the skilled artisan, is triethylene diamine.

The molding of M.E.P. according to the inventive process is illustratedin the Examples that follow.

Into a mixing head are fed all the reaction partners:

Q-PUR-1 (base 1)

Q-PUR-2 (base 2)

SOLUTION 1 (catalyst)

SOLUTION 2 (chain lengthener)

SOLUTION 3 (foaming agent)

The tanks containing the bases 1 and 2 are thermoregulated at atemperature of 50°-60° C. and provided with a moisture trap.

A gear pump, having a volume proportional to the quantity of productmass used per unit of time, maintains the base (1 or 2) in continuousand constant circulation between the tank and the mixing head.

The tanks containing the additives are thermoregulated at a temperatureof 20°-30° C. and provided with moisture traps.

In this case too it will be a gear pump, yet having a volume twentytimes lower than the previously cited one, that keeps the recycling inthe head.

The flow rate of all these pumps is governed by a manager program of themolding cycle. The program, stored in a processor's memory, stabilizes,according to demand, the quantities of the various partners which takepart in the reaction.

Shortly before injection, the speed of the motors connected to the pumpsis adjusted by the processor's interfaced control cards to the r.p.m.snecessary for the specific situation. At the command "START-INJECTION"only the valves open up that correspond to the materials that have totake part in the reaction producing that given type of polyurethane. Thevalves remain open so as to interrupt recycling and to feed the reactionpartners into the mixing zone for the time required to fill the mold.

The products crossing the mixing zone come into close contact throughthe use of a mechanical impeller.

The ejection from the head occurs through an orifice at the extremity ofthe head itself.

Once the injection is finished, the dedicated software redirects theoutput according to the program and the cycle continues, allowing forthe production of a continuously differentiated series of M.E.P.

EXAMPLE 18

An M.E.P. of low specific gravity, having sufficient compressivestrength to permit its use for producing shoe bottoms, is nowexemplified.

    ______________________________________                                        DOSAGE OF THE COMPONENTS:                                                                         flow rate                                                                     (g/s)                                                     ______________________________________                                        SOLUTION 1 - Catalyst 0.32                                                    SOLUTION 3 - Foaming Agent                                                                          0.26                                                    SOLUTION 2 - Chain Lengthener                                                                       2.75                                                                          3.33                                                    BASE 1                45.50                                                   BASE 2                0.00                                                    TOTAL BASES           45.50                                                   TOTAL FLOW RATE       48.83                                                   ______________________________________                                    

This M.E.P. has the following chemical composition:

    ______________________________________                                               MD1     35.50                                                                 Polyester 1                                                                           57.67                                                                 Polyester 2                                                                           0.00                                                                  MEG (*) 6.47                                                                  Dabco   0.20                                                                  Water   0.16                                                                  TOTAL   100.00                                                         ______________________________________                                    

EXAMPLE 19

An M.E.P. of low specific weight, with such characteristics of softnessas to permit its use for producing innersoles for footwear, is nowexemplified:

    ______________________________________                                        DOSAGE OF THE COMPONENTS:                                                                          flow rate                                                                     g/s                                                      ______________________________________                                        SOLUTION 1 - Catalyst  0.23                                                   SOLUTION 3 - Foaming Agent                                                                           0.37                                                   SOLUTION 2 - Chain Lengtherener                                                                      0.01                                                   Total Additives        0.61                                                   BASE 1                 13.65                                                  BASE 2                 14.74                                                  TOTAL BASES            28.39                                                  TOTAL FLOW RATE        29.00                                                  ______________________________________                                    

This M.E.P. has the following chemical composition:

    ______________________________________                                               MDI     20.93                                                                 Polyester 1                                                                           29.14                                                                 Polyester 2                                                                           47.83                                                                 MEG (*)  1.48                                                                 Dabco    0.24                                                                 Water    0.38                                                                 TOTAL   100.00                                                         ______________________________________                                    

EXAMPLE 20

An M.E.P., with specific gravity greater than 1, very resilient,particularly suitable for producing anti-slip surfaces exposed toclimatically critical environments (temperatures between -20° and -50°C.), is now exemplified.

    ______________________________________                                        DOSAGE OF THE COMPONENTS:                                                                         flow rate                                                                     (g/s)                                                     ______________________________________                                        SOLUTION 1 - Catalyst 0.14                                                    SOLUTION 3 - Foaming Agent                                                                          0.00                                                    SOLUTION 2 - Chain Lengthener                                                                       0.72                                                    Total additives       0.86                                                    BASE 1                13.65                                                   BASE 2                14.74                                                   TOTAL BASES           28.39                                                   TOTAL FLOW RATE       29.25                                                   ______________________________________                                    

This M.E.P. has the following chemical composition:

    ______________________________________                                               MDI     20.75                                                                 Polyester 1                                                                           28.90                                                                 Polyester 2                                                                           47.43                                                                 MEG (*)  2.78                                                                 Dabco    0.14                                                                 Water    0.00                                                                 TOTAL   100.00                                                         ______________________________________                                    

EXAMPLE 21

An M.E.P., with specific gravity greater than 1, very stiff,particularly suitable for being worked with machine tools and cut intoslabs, cylinders, and so forth, is now exemplified.

    ______________________________________                                        DOSAGE OF THE COMPONENTS:                                                                         flow rate                                                                     (g/s)                                                     ______________________________________                                        SOLUTION 1 - Catalyst 0.28                                                    SOLUTION 3 - Foaming Agent                                                                          0.00                                                    SOLUTION 2 - Chain Lengthener                                                                       3.23                                                    Total additives       3.51                                                    BASE 1                45.50                                                   BASE 2                0.00                                                    TOTAL BASES           45.50                                                   TOTAL FLOW RATE       49.01                                                   ______________________________________                                    

This M.E.P. has the following chemical composition:

    ______________________________________                                               MDI     35.37                                                                 Polyester 1                                                                           57.47                                                                 Polyester 2                                                                           0.00                                                                  MEG (*) 6.99                                                                  Dabco   0.17                                                                  Water   0.00                                                                  TOTAL   100.00                                                         ______________________________________                                    

EXAMPLE 22

An M.E.P., specifically produced for making the soles of sport shoesthat require particular stress resistance properties, is nowexemplified.

    ______________________________________                                        DOSAGE OF THE COMPONENTS:                                                                         flow rate                                                                     (g/s)                                                     ______________________________________                                        SOLUTION 1 - Catalyst 0.23                                                    SOLUTION 3 - Foaming Agent                                                                          0.19                                                    SOLUTION 2 - Chain Lengthener                                                                       1.64                                                    Total additives       2.06                                                    BASE 1                29.57                                                   BASE 2                7.37                                                    TOTAL BASES           36.94                                                   TOTAL FLOW RATE       39.00                                                   ______________________________________                                    

This M.E.P. has the following chemical composition:

    ______________________________________                                               MDI     30.01                                                                 Polyester 1                                                                           46.95                                                                 Polyester 2                                                                           17.78                                                                 MEG (*)  4.95                                                                 Dabco    0.18                                                                 Water    0.14                                                                 TOTAL   100.00                                                         ______________________________________                                    

The M.E.P.'s that can be made with the process of the instant inventioncan be used in the widest range of fields such as, e.g., shoemanufacturing in order to produce polyurethane bottoms for any kind ofshoe, innersoles, leggings, footwear and sandals; in the marine sectorfor producing the inner shells of ships, buoys, anti-slip carpets,handles and handrails; in road works to produce expansion joints,obstacles for reducing the speed of vehicles and removable buffers; inthe car industry to produce bumpers, steering wheels, protective sumpsand panellings; in the sector of technical articles to produce joints,suckers, gears, shock absorbers and protection gloves and in thefurniture sector to produce furniture, frames, paving tiles anddecorations.

We claim:
 1. In a process for molding microcellular elastomericpolyurethane articles wherein reactants are brought together in a mixinghead according to known methods, the improvement comprising:reacting afirst type quasi-polyurethane having a molecular weight of from 600 to2200 and a free isocyanate group percent content of from 14 to 3.8, withat least one of a second type of quasi-polyurethane, having a molecularweight of from 3000 to 8000 and a free hydroxyl group percent content offrom 1.13 to 0.48, and a glycol and optionally in the presence of water.2. A molding process according to claim 1, wherein said microcellularelastomeric polyurethane is made by reacting a first typequasi-polyurethane, having a molecular weight of from 700 to 1100 and afree isocyanate group percent content of from 12 to 7.6, with a secondtype quasi-polyurethane having a molecular weight of from 3750 to 4500and a free hydroxyl group percent content of from 0.9 to 0.75, andwater.
 3. A molding process according to claim 1, wherein saidmicrocellular elastomeric polyurethane is made by reacting a first typequasi-polyurethane, having a molecular weight of from 700 to 1100 and afree isocyanate group percent content of from 12 to 7.6, with a secondtype quasi-polyurethane, having a molecular weight of from 3750 to 4500and a free hydroxyl group percent content of from 0.9 to 0.75, a glycoland water.
 4. A molding process according to claim 1, wherein saidmicrocellular elastomeric polyurethane is made by reacting a first typequasi-polyurethane, having a molecular weight of from 700 to 1100 and afree isocyanate group percent content of from 12 to 7.6, with a secondtype quasi-polyurethane having a molecular weight of from 3750 to 4500and a free hydroxy group percent content of from 0.9 to 0.75, with aglycol.
 5. A molding process according to claim 1, wherein saidmicrocellular elastomeric polyurethane is made by reacting a first typequasi-polyurethane, having a molecular weight of from 700 to 1100 and afree isocyanate group percent content of from 12 to 7.6, with a secondtype quasi-polyurethane having a molecular weight of from 3750 to 4500and a free hydroxyl group percent content of from 0.9 to 0.75.
 6. Amolding process according to claim 1, wherein said microcellularelastomeric polyurethane is made by reacting a first typequasi-polyurethane, having a molecular weight of from 700 to 1100 and afree isocyanate group percent content of from 12 to 7.6, with a glycoland water.
 7. A molding process according to claim 1, wherein saidmicrocellular elastomeric polyurethane is made by reacting a first typequasi-polyurethane, having a molecular weight of from 700 to 1100 and afree isocyanate group percent content of from 12 to 7.6, with a glycol.8. A molding process according to any one of claims 1 to 7, wherein saidfirst type quasi-polyurethane, having a molecular weight of from 600 to2200 and a free isocyanate group percent content of from 14 to 3.8, ismade by reacting, according to known methods, a diphenylmethanediisocyanate with a saturated polyester having a molecular weight offrom 1500 to 2500, in a molar ratio of 1:2.
 9. A molding processaccording to any one of claims 1 to 7, wherein said first typequasi-polyurethane, having a molecular weight of from 600 to 2200 and afree isocyanate group percent content of from 14 to 3.8, is made byreacting, according to known methods, a diphenylmethane diisocyanatewith a polyether having a molecular weight of from 1500 to 2500, in amolar ratio of 1:2.